1. Field of the Invention
This invention relates to a new zeolite designated ZSM-48 and to its use in catalytic hydrocarbon conversion processes, and more particularly to its use in selective production of para-disubstituted aromatics.
2. Description of the Prior Art
The disproportionation of aromatic hydrocarbons in the presence of zeolite catalysts has been described in the Oil and Gas Journal, Vol. 69, No. 48 (1971).
U.S. Pat. Nos. 3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961 show vapor-phase disproportionation of toluene over various catalysts.
Alkylation of aromatic hydrocarbons with an olefin in the presence of a crystalline metallic aluminosilicate having uniform pore openings of about 6 to 15 Angstrom units is described in U.S. Pat. No. 2,290,607. U.S. Pat. No. 3,251,897 describes alkylation of aromatic hydrocarbons in the presence of X- or Y-type crystalline aluminosilicate zeolites, specifically such type zeolites wherein the cation is rare earth and/or hydrogen. U.S. Pat. Nos. 3,751,504 and 3,751,506 describe vapor phase alkylation of aromatic hydrocarbons with olefins, e.g. benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst.
In these prior art processes, the xylene product has the equilibrium composition of approximately 24 percent para, 54 percent meta and 22 percent ortho.
The alkylation of toluene with methanol in the presence of a cation exchanged zeolite Y has been described in the Journal of Catalysis 16, 273-280 (1970). It was reported there that selective production of p-xylene over the approximate temperature range of 200.degree. to 275.degree. C. with the maximum yield of p-xylene in the mixture of xylenes, i.e. about 50 percent of the xylene product mixture, being observed at 225.degree. C. Higher temperatures were reported to result in an increase in the yield of m-xylene and a decrease in the production of para- and ortho-xylene.
Transalkylation of toluene using a catalyst of faujasite or mordenite, a Group VIII metal, such as platinum, and an additional component of arsenic, antimony, bismuth, selenium, tellurium or compounds thereof is described in U.S. Pat. No. 3,527,824.
Of the xylene isomers, i.e. ortho, meta and para-xylene, meta-xylene is the least desired product, with ortho and para-xylene being the more desired products. p-xylene is of particular value being useful in the manufacture of terephthalic acid which is an intermediate in the manufacture of synthetic fibers, such as "Dacron". Mixtures of xylene isomers, either alone or in further admixture with ethylbenzene, generally containing a concentration of about 24 weight percent para-xylene in the equilibrium mixture, have previously been separated by expensive superfractionation and multistage refrigeration steps. Such processes have high operating costs and provide limited yield.
The ZSM-5 class of zeolite catalysts have been shown to be shape selective. This shape selectivity can be further enhanced by the use of very large crystals, impregnation with Mg and P to reduce zeolite pore openings and by coke selectivation. These modified zeolite catalysts have been very effective in such reactions as selective toluene disproportionation which yields predominantly p-xylene as the product and toluene-ethylene alkylation yielding primarily p-ethyltoluene. These modification procedures are quite complex.